This innovation relates to a machine for making liquid or semi-liquid food products, specifically cold products such as, but not limited to, for example, slush drinks, sorbets dessert creams, artisan gelatos or soft ice creams, where the refrigeration system responsible for cooling the liquid product is internally provided with a flooded evaporator instead of a dry evaporator.
Hence, the industrial context which this disclosure addresses is that of machines for making (cold) liquid or semi-liquid products.
In these industrial applications, there is an increasingly widespread need to improve the efficiency of the machines, in particular the energy efficiency, and thus the heat exchange efficiency of the refrigerating systems of the machines.
It is known that the refrigeration systems of machines for making cold, liquid or semi-liquid food products are of the “dry” type. The term “dry” in this context is used to mean the feature of the refrigeration system whereby the heat exchanger fluid flowing out of the evaporator is in the form of superheated vapor, that is to say, free of the liquid phase, and can therefore be directed into the compressor without the risk of damaging the compressor with the liquid droplets dispersed in the vapor. Experiments conducted by the Applicant have shown that the total heat-exchange coefficient is directly proportional to the density of the fluids in contact: the higher the percentage of vapor relative to liquid, the lower the heat exchange efficiency. It may also be observed that until it reaches the state of saturated vapor, the heat exchanger fluid has the same temperature. That is because the quantity of heat extracted is used for the change of phase. Thus, the difference in temperature between the heat exchanger fluid and the surroundings decreases at a first decreasing rate. When the heat exchanger fluid reaches the state of saturated vapor, the full amount of heat transferred from it to the surroundings is used to increase the temperature which leads to an increase in the decreasing rate of the temperature difference between the heat exchanger fluid and the surroundings.